Streptococcus pneumoniae is a well known human pathogen and a major etiologic agent for pneumonia, meningitis, otitis media as well as sepsis, among primarily young children and older adults. S. pneumoniae has been divided into ninety serotypes based on its expression of serologically distinct carbohydrate capsules. Antibodies to a capsular polysaccharide (PS) may provide protection against pneumococci expressing the same capsular serotype. Currently available pneumococcal vaccines contain a mixture of capsular PS of multiple serotypes. For example, one pneumococcal vaccine (called PS vaccine) contains capsular PS from twenty-three commonly found serotypes. The most recently developed type of vaccine (called conjugate vaccine) contains capsular PS from seven to thirteen serotypes that are conjugated to a protein molecule. A seven-valent conjugate vaccine was introduced in 2000 for clinical use in the USA and has reduced the incidence of invasive pneumococcal diseases in children and in adults.
The distribution of pneumococcal serotypes is useful in estimating vaccine efficacy. Ideally, an effective pneumococcal vaccine would reduce the prevalence of pneumococci expressing the serotypes included in the vaccine and leave the prevalence of the pneumococci expressing non-vaccine serotypes the same. In reality, the prevalence of the pneumococci expressing non-vaccine types increases to replace those expressing the vaccine serotypes. Further, the prevalence of specific serotypes may change over time for unknown reasons. Consequently, accurate and efficient serotyping of pneumococcal isolates is important for monitoring the efficacy of pneumococcal vaccines. Indeed, identifying emerging pneumococcal serotypes and producing more efficacious pneumococcal vaccines remain crucial goals in public health.